Turbine blade rail damper

ABSTRACT

A device for damping of vibratory energy in the blades of rotor assemblies during operation where the blades have a shroud attached thereto with at least one sealing rail extending radially outward from the shroud to an outer diameter surface. A damper element is attached to the turbine blade sealing rail extending radially inward from the rail outer diameter surface along rail sides to maintain the damper element out of the flow of gas and positioned at a radial location on the blade for damping.

BACKGROUND

This invention relates to rotor blades and specifically to the mechanical damping of vibratory energy in the blades of rotor assemblies during operation. Rotor assemblies are used in a variety of turbo-machines, such as turbines and compressors. During operation, fluid forces induce vibratory stresses on the blades, resulting in high cycle fatigue and potential failure of the blades. Dampers, commonly frictional dampers, are utilized to reduce the magnitude of these dynamic stresses, thereby increasing operational life of the blades.

Typically the most effective frictional dampers are located on the turbine blade shroud. The shroud is located at the radial tip of the rotor blade adjacent the stationary housing. During operation, centrifugal forces urge the damper into frictional contact with its adjacent blade shroud. This contact reduces the relative motion between the adjacent blades, thereby reducing the vibratory stresses on the blades during operation. Frictional damping is effective so long as relative motion exists between the damper and the blade. When the rotor speed becomes high, typical flat plate shroud dampers become too heavy and the frictional damper sticks to the shroud due to friction thereby reducing its effectiveness. Typical lighter weight damper designs consist of loss fitting rivets. These rivets are hard to form due to the many tight tolerance features required and they are exposed to the main gas flow.

Other efforts to reduce vibrational damage not only are structurally deficient in affecting the clearances of the shroud, they are subject to fatigue that further reduces their effectiveness.

Conventional shrouds typically include one or more sealing rails that extend radially outward from the shroud in close proximity to the stationary housing and typically extend continuously across the top surface of the shroud between first and second circumferential sides. Typical previous shroud frictional dampers are retained by extra features added to the shroud. These added features are located on the shroud at the furthest distance from blade which increases the shroud overhung weight. These added features increase the centrifugal induced bending stress in the shroud which may result in potential failure of the rotor assembly due to high cycle fatigue. To counteract this, the shroud thickness must be increased. This increase in shroud thickness also results in higher centrifugal stress in the blade at the blade's two critical locations, the blade shank and firtree.

What is needed is a way to place any damper out of the main gas flow of turbo-machines without adversely affecting the function of the shroud.

SUMMARY

The present invention relates to a damper arrangement on the sealing rail of turbo-machine shrouds where the damper in the rail is outside of the main gas flow. This invention uses the existing rail and requires no modification to the shroud to retain the damper. The rail damper comprises a shim stock having its ends oriented to function with specific shroud rail configurations. The present invention does not require any special retainment features. Retainment features add weight to the shroud and result in lower shroud and blade safety factors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating one embodiment of the present invention in a rotor assembly used in turbo-machines, showing turbine blades having shrouds with rails and damper elements.

FIG. 2 a is a perspective view of the embodiment in a shroud rail.

FIG. 2 b is an enlarged perspective view of the damper used in FIG. 1.

FIG. 2 c is an enlarged perspective view of the slot in the shroud and rail in FIG. 2 a.

FIG. 2 d is an end view of the damper in the slot of FIG. 2 c.

FIG. 3 a perspective view of another embodiment of this invention in a shroud rail.

FIG. 3 b is an enlarged perspective view of the damper used in FIG. 3 a.

FIG. 3 c is an enlarged perspective view of the slot in the shroud and rail in FIG. 3 a.

FIG. 3 d is an end view of the damper in the slot of FIG. 3 c.

FIG. 4 a perspective view of another embodiment of this invention in a shroud rail.

FIG. 4 b is an enlarged perspective view of the damper used in FIG. 4 a.

FIG. 4 c is an enlarged perspective view of the slot in the shroud and rail in FIG. 4 a.

FIG. 4 d is an end view of the damper in the slot of FIG. 4 c.

FIG. 5 a perspective view of another embodiment of this invention in a shroud rail.

FIG. 5 b is an enlarged perspective view of the damper used in FIG. 5 a.

FIG. 5 c is an enlarged perspective view of the slot in the shroud and rail in FIG. 5 a.

FIG. 5 d is an end view of the damper in the slot of FIG. 5 c.

FIG. 6 a perspective view of another embodiment of this invention in a shroud rail.

FIG. 6 b is an enlarged perspective view of the damper used in FIG. 6 a.

FIG. 6 c is an enlarged perspective view of the slot in the shroud and rail in FIG. 6 a.

FIG. 6 d is an end view of the damper in the slot of FIG. 6 c.

FIG. 7 a perspective view of another embodiment of this invention in a shroud rail.

FIG. 7 b is an enlarged perspective view of the damper used in FIG. 7 a.

FIG. 7 c is an enlarged perspective view of the slot in the shroud and rail in FIG. 7 a.

FIG. 7 d is an end view of the damper in the slot of FIG. 7 c.

FIG. 8 a perspective view of another embodiment of this invention in a shroud rail.

FIG. 8 b is an enlarged perspective view of the damper used in FIG. 8 a.

FIG. 8 c is an enlarged perspective view of the slot in the shroud and rail in FIG. 8 a.

FIG. 8 d is an end view of the damper in the slot of FIG. 68 c.

DETAILED DESCRIPTION

FIG. 1 shows a perspective view of an assembly, 10 generally, of a pair of turbine blades 11 a and 11 b of a turbo-machine such as a gas turbine engine. Blades 11 a and 11 b include firtrees 11 a and 11 b, blade shanks 12 a and 12 b, platforms 13 a and 13 b, airfoils 15 a and 15 b, shrouds 17 a and 17 b, upstream rails 19 a and 19 b, and downstream rails 20 a and 20 b, respectively. Airfoils 15 a and 15 b extend radially out from platforms 13 a and 13 b to shrouds 17 a and 17 b. Shrouds 17 a and 17 b include upstream rails 19 a and 19 b and downstream rails 20 a and 20 b extend out radially outward in close proximity to a stationary housing (of conventional design, not shown). Rails 19 a, 19 b, 20 a and 20 b typically extend continuously across the top surface of shrouds 17 a and 17 b between first and second circumferential sides. Rail damper 21 is placed on rail 19 at a point remote from the main gas flow in the turbo-machine. Damper 21 is radially inward from the rail end surface 19 a. Damper 21 is shown bridging the gap between successive upstream rail portions of 19 a and 19 b at junction 22.

FIG. 1 shows two blades 11 a and 11 b to illustrate the positioning of damper 21 at junction 22. Also shown is another damper 21 at the right end of rail 19 b for positioning between rail 19 b and a corresponding upstream rail of a blade that will be positioned adjacent blade 19 b.

Damper element 21 may be any shape that provides a fit on the rail, with a generally “U” shape being shown. The sides of the “U” shape may extend radially up or down, depending on the configuration of rail 19. The use of the “U” shape allows for simple manufacture and installation. Damper 21 may be any material, such as steel or other metals, ceramics and other materials. Damper 21 material should be selected to have a light weight when possible.

FIG. 2 a is an enlarged perspective view showing the details of the relationship between shroud 17 a and rails 19 a and 19 b. Damper 21 is seen in FIG. 2 b as having a full round shape, with a flat center portion 21 a and both ends 21 b and 21 c extending up to engage rail 19 b. FIG. 2 c shows damper slot 23 with a full round slot 23 a to accept and hold damper 21. FIG. 2 d shows damper 21 in slot 23 in the operating position.

FIG. 3 a is an enlarged perspective view showing the details of an alternative relationship between shroud 17 a and rails 19 a and 19 b. Damper 21 is seen in FIG. 3 b as having a full round shape, with a flat center portion 21 a and both ends 21 b and 21 c fully rounded to engage rail 19 b. FIG. 3 c shows damper slot 23 with a full round slot 23 a to accept and hold damper 21. FIG. 3 d shows damper 21 in slot 23 in the operating position.

FIG. 4 a is an enlarged perspective view showing the details of another alternative relationship between shroud 17 a and rails 19 a and 19 b. Damper 21 is seen in FIG. 4 b as having an O.D. round shape, with a flat center portion 21 a and both ends 21 b and 21 c having a rounded O.D. to engage rail 19 b. FIG. 4 c shows damper slot 23 with an undercut slot 23 a to accept and hold damper 21. FIG. 4 d shows damper 21 in slot 23 in the operating position.

FIG. 5 a is an enlarged perspective view showing the details of another alternative relationship between shroud 17 a and rails 19 a and 19 b. Damper 21 is seen in FIG. 5 b as having an O.D. round shape large enough to accommodate the axial stops 19 a and 19 b, with a flat center portion 21 a and both ends 21 b and 21 c having a size suitable to engage axial stops 19 a and 19 b. FIG. 5 c shows damper slot 23 with an undercut slot 23 a to accept and hold damper 21. FIG. 5 d shows damper 21 in slot 23 in the operating position.

FIG. 6 a is an enlarged perspective view showing the details of another alternative relationship between shroud 17 a and rails 19 a and 19 b. Damper 21 is seen in FIG. 6 b as having a full round shape, with a flat center portion 21 a and both ends 21 b and 21 c to engage rail 19 b. FIG. 6 c shows damper slot 23 with a round slot 23 a to accept and hold damper 21. FIG. 6 d shows damper 21 in slot 23 in the operating position.

FIG. 7 a is an enlarged perspective view showing the details of another alternative relationship between shroud 17 a and rails 19 a and 19 b. Damper 21 is seen in FIG. 7 b as having a full round shape, with a flat center portion 21 a and both downward facing ends 21 b and 21 c to engage rail 19 b. FIG. 7 c shows damper slot 23 with portions of shroud 17 a and 17 b relieved to accept and hold damper ends 21 b and 21 c. FIG. 7 d shows damper 21 in slot 23 in the operating position.

FIG. 8 a is an enlarged perspective view showing the details of another alternative relationship between shroud 17 a and rails 19 a and 19 b. Damper 21 is seen in FIG. 8 b as having a full round shape, with a flat center portion 21 a and both downward facing ends 21 b and 21 c to engage rail 19 b. FIG. 8 c shows damper slot 23 wider to accept and hold damper ends 21 b and 21 c without having any part of shroud 17 being removed. FIG. 8 d shows damper 21 in slot 23 in the operating position.

In all of the embodiments shown herein, the damper is designed to engage the sealing rail of a shroud facing inward from the rail outer surface to maintain the damper element out of the flow of gas and at the most effective radial location on the blade. Damping is affected without any lessening of the functionality of the rails or the shroud. Similar dampers may also be placed on downstream rails since alteration of the shroud is not needed.

The invention has been shown in association with a firtree bladed rotor. The invention is also suitable for use with other rotor configurations such as an integrally bladed rotor, for example.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A device for damping of vibratory energy in turbine blades of rotor assemblies during operation, comprising: a first turbine blade having a shroud with a sealing rail, the sealing rail having a generally circumferential slot at each end of the rail; a second turbine blade adjacent the first blade and having a shroud with a sealing rail, the sealing rail having a generally circumferential slot at each end of the rail such that a slot at the end of the first blade rail nearest the second blade is adjacent and opposing a slot at the end of the second blade rail nearest the first blade; a damper element positioned in and extending between the adjacent slots of the first blade rail and the second blade rail.
 2. The device of claim 1, wherein the damper element is made from metal or ceramic.
 3. The device of claim 1, wherein the slots at the ends of the first and second turbine blade are positioned between the shroud and the outer surface of the rail to keep the damper element out of the flow of gas.
 4. The device of claim 1, wherein the damper element is generally “U” shaped with the bottom of the “U” engaging the back of the slots and the sides of the “U” extend along the sides of the rail portion having the slots.
 5. The device of claim 4, wherein the sides of the “U” extend radially upward on the side rails.
 6. The device of claim 1, wherein the sides of the “U” extend radially downward on the side rails.
 7. The device of claim 1, wherein the slot is undercut at the inside end of the slot to further engage the damper element.
 8. The device of claim 1, wherein the sealing rail further includes axial stops on the rail sides for engaging the damper element.
 9. A rotor for use with a turbine having a plurality of blades extending radially outward, comprising: a plurality of shrouds, each shroud being positioned radially outward of and attached to one of the blades a plurality of sealing rails, each sealing rail of a radially outward side of each shroud, the sealing rail having a generally circumferential slot at each end of the rail; and a plurality of damper elements, each damper element being positioned in and extending between adjacent slots of opposing ends of adjacent blade rails.
 10. The rotor of claim 9, wherein the damper element is made from metal or ceramic.
 11. The rotor of claim 9, wherein the sealing rail further includes axial stops on the rail sides for engaging the damper element.
 12. The rotor of claim 9, wherein the damper element is generally “U” shaped with the bottom of the “U” engaging the back of the slots and the sides of the “U” extend along the sides of the rail portion having the slots.
 13. The rotor of claim 12, wherein the sides of the “U” extend radially upward on the side rails.
 14. The rotor of claim 12, wherein the sides of the “U” extend radially downward on the side rails.
 15. The rotor of claim 9, wherein the slot is undercut at the inside end of the slot to further engage the damper element.
 16. A rotor for use with a turbine, the rotor, comprising: a plurality of blades extending radially outward, each blade having a shroud positioned at a radially outward end of the blade and containing a sealing rail, each sealing rail having a generally circumferential slot at each end of the rail; and a plurality of damper elements made from metal or ceramic, each damper element being positioned in the adjacent opposing slots of adjacent sealing rails, each damper element being generally “U” shaped with the bottom of the “U” engaging the back of the slots and the sides of the “U” extend along sides of the sealing rail.
 17. The device of claim 16, wherein the “U” shaped damper element sides extend radially upward on the sealing rail sides.
 18. The device of claim 16, wherein the “U” shaped damper element sides extending radially downward on the sealing rail sides.
 19. The device if claim 16, wherein a portion of the shroud has been relieved proximate the location of the sides of the damper element.
 20. The device of claim 16, wherein the slot is undercut at the inside end of the slot to further engage the damper element. 